North American bird populations are not only declining, but they’re also shrinking faster with each passing year – particularly in regions shaped by intensive agriculture, according to a new study. Centuries of human impacts, including land use change, agricultural intensification, overexploitation, and pollution, have drastically reshaped the natural world, leading to population declines for many wildlife species worldwide. Although these declines are widely recognized, whether these losses are speeding up year over year, as well as the factors driving this potential acceleration, remain poorly understood. Here, François Leroy and colleagues investigate these trends among North American bird populations. Leroy et al. analyzed data from 1,033 migration survey routes in the North American Breeding Bird Survey, examining 261 bird species between 1987 and 2021. Using advanced statistical modeling, the authors estimated population dynamics over time, revealing an average continent-wide decline in bird abundance. According to the findings, the steepest losses were concentrated in the southern and warmer regions of North America, with hotspots of accelerating decline in the Mid-Atlantic, Midwest, and California – areas that closely align with regions of intensive agriculture. Leroy et al. also found that 47% of species studied (122 species) show significant population declines, 63 of which are deteriorating at an accelerated rate. 67 species show declines that outpace population recruitment, suggesting deeper demographic strain. 

Media may wish to note an exclusive feature this week from Science’s news department on bird declines in tropical forests, embargoed for Wednesday Feb 25 at noon US ET. Please reach scipak@aaas.org for a PDF of the embargoed story.

Though previous research has shown that bird populations are declining across North America, a new study is the first to show that the pace of loss has picked up speed since the mid-1980s in three regions: the Midwest, California and Mid-Atlantic states. After these hotspots of accelerated bird decline were revealed, researchers looked for factors that could explain the difference in the rates of decline, examining climate measures and human activity-related data. A top predictor of where the accelerated abundance loss occurred became clear, overlapping with locations of agriculture intensity as indicated by the extent of cropland and the use of fertilizer and pesticides.